It is known that N-(trans-4-isopropylcydohexanecarbonyl)-D-phenylalanine of the following formula: ##STR1## (hereinafter referred to as "compound [1]) exhibits an excellent effect of lowering the blood sugar level when it is taken orally, and is thus usable as a medicine for diabetes [Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J. P. KOKOKU") No. Hei 4-15221].
However, it was found that when compound [1] is orally taken before or after a meal for the purpose of preventing the blood sugar level after the meal from rising, the bioavailability of the compound is lowered.